As a method for qualitatively or quantitatively measuring a test substance existing in a biological sample such as urine or blood, immunoassay has been widely used. Among such immunoassay methods, an immunochromatography has been commonly used because it involves simple operations and it enables measurement in a short time. As a method for supplying two types of liquids to a membrane, the method described in JP Patent Publication (Kokai) No. 10-104236 A (1998) has been known.
At present, a common immunochromatography is problematic in that an antigen is not detected due to low sensitivity and the result becomes false negative. Thus, it is desired to develop an immunochromatography with a higher sensitivity. A silver amplification method has been known as a method for realizing a high sensitivity of an immunochromatography using a gold colloid as a labeling substance. According to JP Patent Publication (Kokai) No. 2002-202307 A, after a sample solution has been supplied, a solution used for silver amplification is added dropwise to a test line portion for amplification, so as to achieve a high sensitivity. However, in general, when such solutions used in silver amplification are mixed up, the mixed solution becomes extremely poor in terms of preservation quality. Thus, in the case of the silver amplification solution used in the silver amplification method described in JP Patent Publication (Kokai) No. 2002-202307 A, two types of liquids, which have been preserved separately, are mixed, and the thus mixed solution is then added dropwise to a test line portion, thereby performing silver amplification.